Whereas, when die-casting aluminum base alloy is used, the mechanical strength of the die-casted product tends to be uneven in a great extent since the tensile strength of the die-casting aluminum base alloy is low as much as 20 to 30 Kgf/mm.sup.2, particularly 10 to 20 Kgf/mm.sup.2 at 0.2% proof stress, and therefore, it is not possible to expect to obtain the die-casted product with high mechanical strength. Furthermore, the toughness of the die-casting aluminum base alloy is inferior, thus the industrial use of the die-casting aluminum base alloy has been limited.
On the other hand, traditional die-casting aluminum base alloy, for example, JIS-AC2B or AC4C is heat treated to improve mechanical strength at 500.about.540.degree. C. However, steel parts deteriorates its mechanical strength of hardness when the aluminum base alloy has inserted steel parts. In other wards, traditional die-casting aluminum base alloy having inserted steel parts can not be heat treated.
Further more, traditional die-casting aluminum base alloy, sometimes, for example, typically JIS-ADC12, blisters when heated at more than 500.degree. C. and then surface state of the alloy deteriorates.